Misfire detecting system for engine

Abstract

A misfire detecting system for an engine of a vehicle that detects a misfire of the engine is provided, which includes a processor. The processor determines whether a misfire has occurred by examining whether a fluctuation of a crank angle of the engine is equal to or greater than a determination reference value, acquires a value relating to a density of intake air introduced into the engine, and adjusts the determination reference value according to the value related to the density.

What is claimed is: 
     
       1. A misfire detecting system for an engine of a vehicle that detects a misfire of the engine, the misfire detecting system comprising:
 a crank angle sensor configured to detect a crank angle of a crank shaft of the engine; 
 an intake air temperature sensor configured to detect a temperature of an intake air; and 
 a processor operatively coupled to the crank angle sensor and the intake air temperature sensor and configured to: 
 calculate a crank angular acceleration fluctuation based on the crank angle detected by the crank angle sensor; 
 determine whether a misfire has occurred by examining whether the crank angular acceleration fluctuation is equal to or greater than a determination reference value, wherein 
 the determination reference value is set to a first value when the detected temperature of the intake air is a first temperature; 
 the first value is higher than a second value that is set when the detected temperature is a second temperature, which is higher than the first temperature so as to prevent a false determination of the misfire; and 
 the processor outputs an indication to alert an abnormality relating to the misfire of the engine, when the misfire is determined. 
 
     
     
       2. The misfire detecting system of  claim 1 , wherein the processor changes the determination reference value based on an engine speed and an engine load, and a change amount of the determination reference value in accordance with the temperature of the intake air is larger when the engine speed is high, compared to when the engine speed is low. 
     
     
       3. The misfire detecting system of  claim 1 , wherein the processor adjusts the determination reference value between the first and second values according to the temperature of the intake air when the temperature of the intake air is within a given range between the first temperature and the second temperature. 
     
     
       4. The misfire detecting system of  claim 1 , wherein the engine is provided with a turbocharger. 
     
     
       5. The misfire detecting system of  claim 1 , wherein the determination reference value is set by the detected temperature so as to take into consideration an intake air density. 
     
     
       6. The misfire detecting system of  claim 1 , wherein outputting the indication is accomplished by turning on an alarm lamp. 
     
     
       7. A misfire detecting system for an engine of a vehicle that detects a misfire of the engine, the misfire detecting system comprising: a crank angle sensor configured to detect a crank angle of a crank shaft of the engine; and a processor operatively coupled to the crank angle sensor and configured to:
 obtain a temperature of an intake air; 
 calculate a crank angular acceleration fluctuation based on the crank angle detected by the crank angle sensor; 
 determine whether a misfire has occurred by examining whether the crank angular acceleration fluctuation is equal to or greater than a determination reference value, wherein 
 the determination reference value is set to a first value when the obtained temperature of the intake air is a first temperature; 
 the first value is higher than a second value that is set when the obtained temperature is a second temperature, which is higher than the first temperature so as to prevent a false determination of the misfire; and 
 the processor outputs an indication to alert an abnormality relating to the misfire of the engine, when the misfire is determined. 
 
     
     
       8. The misfire detecting system of  claim 7 , wherein the temperature of the intake air is obtained from an intake air temperature sensor. 
     
     
       9. The misfire detecting system of  claim 7 , wherein outputting the indication is accomplished by turning on an alarm lamp.